We have continued our characterization of a putative neutralization escape mutant of HBV that emerged in individuals who were vaccinated against hepatitis B. Two licensed vaccines were investigated for their ability to protect chimpanzees against challenge with the S gene mutant. Both recombinant vaccines provided protection against challenge with the mutant virus, suggesting that properly vaccinated individuals are not at risk of infection by the S gene mutant virus. A bi-directional promoter complex was identified within the X gene of HBV, further emphasizing the complex genetic organization of this virus. We have recovered HBV sequences from the blood and liver of patients with chronic HBV infection and liver cancer. These sequences have been compared to determine if there are differences between the core genes circulating within hepatitis B virions and those that are integrated into liver cancer cells. Special emphasis was placed on core gene sequences, since their possible role in hepatocarcinogenesis is controversial. The sequence of HBV strains recovered from patients with fulminant hepatitis B is being determined. They will be compared with published sequences of HBV strains recovered from fulminant cases, since the relative importance of viral and host factors in fulminant hepatitis B has not been established. Hepatitis B virus is being used as a model system for evaluating the new naked nucleic acid approach to vaccine development. Results obtained with various recombinant vectors and immunization protocols are being compared with each other and with extensive experience with other approaches to hepatitis B vaccine development that have been studied previously in the laboratory. Strains of HBV of particular interest (such as from cases of fulminant hepatitis) are being subjected to a new PCR amplification procedure that amplifies virtually the entire genome for recovery of infectious cDNA. The amplified genomes will be sequenced and, possibly, biologically amplified and characterized in chimpanzees. Long term follow up of the NIAID's plasma-derived vaccine, developed in 1975 and the first successful subunit vaccine, has continued. The vaccine continues to be highly efficacious five years after administration to infants.